1. Technical Field
The invention relates to network systems, such as a video conferencing system. More particularly, the invention relates to a network system that can decrease the load on each end system, as well as on the network itself, by efficiently sending and receiving media data, where the media data processing capability or the media presentation format differs between the various end systems that are connected to the network.
2. Description of the Prior Art
End systems that are connected to an electronic network typically have different hardware and software processing capabilities for media data, such as video data and audio data. It is usually necessary in a network that includes a first end system which conforms to a first media data processing standard, and that includes a second end system which conforms to a different processing standard, for the end system that is receiving the media data to convert the received media data to a format that is consistent with the receiving end system processing standard.
For example, if a sending end system sends MPEG-2 video data to a receiving end system that does not have an MPEG-2 video processing function, then the receiving end system must first convert the MPEG-2 video data to a local video data format, for example, MPEG-1 video data. The format conversion process must be performed by software that is running on the receiving end system central processing unit or by a video processor in the receiving end system. This conversion step increases the processing load at the receiving end system.
In addition, it is not unusual for the media presentation format (e.g. video display format or audio output format) to differ between sending end systems and receiving end systems. For example, a sending end system may display video at a resolution of 1,024 pixels.times.800 pixels, while a receiving end system may display video at a resolution of 800 pixels.times.600 pixels. To display the video in accordance with its display capability, the receiving end system must convert the video data sent by the sending end system (i.e., video having a resolution of 800 pixels.times.1,024 pixels) to video data at the resolution of the receiving end system (i.e., video having a resolution of 600 pixels.times.800 pixels). This conversion step also increases the processing load at the receiving end system.
Another factor that affects media data transfer between a sending end system and a receiving end system is network throughput. Thus, it is often a result that the actual display of video can be significantly delayed when network conditions deteriorate. This is because the receiving end system must wait for a sufficient amount of the video information to arrive via the network if the video is to be displayed at the same resolution as under normal network conditions. This problem is particularly pronounced if the end system is a multitasking system, where network propagation delays result in a decrease in the rate at which the media data are received, and where such decreases in reception rate can result in delays in processes within the end system other than those attributable to the conversion process itself.
A further problem arises when the media data are sent by an end system and are received by a plurality of other end systems, where each receiving end system must convert the media data. The conversion efficiency of media data is poor from the perspective of the entire network system because the conversion process must be separately performed at several end systems. In particular, if media data are sent and received in real time among multiple end systems, e.g., as in video conferencing, the load on each end system described above and on the network is increased. Therefore, it is unlikely that real-time output of the media data can be maintained at the receiving end systems.
In conventional network systems, standards conversion of media may take place either in the end systems or in another entity, as defined in ITU-T recommendation H.231. In such a scheme, a capability exchange occurs prior to media conversion. (See ITU-T recommendation H.242.) In such exchange, each end system declares its media handling capabilities to the MCU, e.g., media encoding and decoding formats and relevant bandwidths.
However, in conventional network systems, the media distribution pattern is very rigid and consequently an end user's options for media consumption is severely restricted.
It would be advantageous to provide a system in which media data are efficiently sent and received across a network, especially where user demands for the media data, processing capabilities, and media presentation formats differ among the end systems connected to the network.